I learned a things:
While it is true that the maximum output of a horse is around 15 horsepower, when you average the output of a horse over the course of a work day it ends up being around a horsepower. Watt defined this amount as “the amount of work required from a horse to pull 150 pounds out of a hole that was 220 feet deep”.
Thank God it wasn’t something arbitrary like pulling a 100 pounds out of a hole that was 250 feet deep.
That almost sounds the metric system /s
I remember reading somewhere that a single horse can actually output 12-14 horsepower. And an average human’s maximum output can be over 1 horsepower.
It’s a stupid unit because it averages long-term output including resting periods, and was inveted for steam engine marketing. At least it reflects the quantity it measures, reducing confusion some people have with kW and kWh.
It’s also based on a mule, not a horse. Specifically, the mules used for towing mine carts.